A bidder legally owns a locker when the unit has gone through the proper auction process and the bidder physically pays the facility. This is why with online auctions bidders usually schedule to pick up the unit the day the auctions ends.
Majority of auctions never go to the price that is owed to the facility. The facilities are aware of this and are losing money with non paying tenants. They put the unit up for auction to have the items removed for new paying tenants. Even if the facility does make more than what is owed they legally have to turn the extra money over to the city or give it back to the tenant.(depending on state laws)
The reality is a lot of tenants do have the money to pay for their unit, but chose not to and wait to see if the facility will actually put it up for auction. When they see it up they freak out and rush to pay off their debt. Others can’t pay their debts and hope that the winning bidder will leave their personal items behind.
The bidder is usually the winner in all this because depending on the items they can make a lot of money out of cheap unit.
I hope this answers your question. Good luck on the hunt.